Propulsion apparatus for ship

ABSTRACT

Provided is a ship propelling apparatus including a rotation shaft on which a rear propeller is fixed; a front propeller rotatably supported on the rotation shaft in front of the rear propeller; and a counter-rotating device through which the rotation shaft passes, which includes a gear box including therein a plurality of gears configured to reverse rotation of the rotation shaft and transfer the reversed rotation to the front propeller, and which is installed in an installation space formed at the rear of a ship. The rotation shaft includes a measurement hole formed to pass through a center of the rotation shaft for centering of the counter-rotating device installed in the installation space; and an individual lubricant path separated from the measurement hole.

TECHNICAL FIELD

The present invention relates to a ship propelling apparatus in whichtwo propellers rotate in opposite directions to generate a propulsiveforce, and a ship including the same.

BACKGROUND ART

In general, a ship propelling apparatus includes one spiral propeller.However, in the case of a propelling apparatus including one propeller,the rotational energy of water streams generated when the propellerrotates cannot be used as a propulsive force, thereby causing a highenergy loss.

A counter-rotating propeller (CRP) is capable of collecting rotationalenergy, which may be lost, as a propulsive force. In the CRP, apropulsive force is generated as two coaxial propellers rotate inopposite directions. The rotational energy of a fluid passing through afront propeller is collected as a propulsive force by a rear propelleras the rear propeller rotates reversely. Thus, the CRP exhibits a higherpropelling performance than a propelling apparatus including onepropeller.

However, since the CRP includes a counter-rotating device enabling twopropellers to rotate in opposite directions, a hollow shaft, etc., theCRP is thus relatively difficult to manufacture, install, maintain, andrepair.

US Patent Publication No. US2011/0033296 (publication date: Feb. 10,2011) and Japanese Patent Application Publication No. sho 62-279189(publication date: Dec. 4, 1987) have disclosed examples of the CRPdescribed above. US Patent Publication No. US2011/0033296 has discloseda CRP including a planetary gear type counter-rotating device and ahollow shaft installed in a hull of a ship. Japanese Patent ApplicationPublication No. sho 62-279189 has disclosed a double counter-rotatingapparatus which is a planetary gear type counter-rotating apparatusinstalled in the tail of a ship.

DISCLOSURE Technical Problem

One or more embodiments of the present invention provide a shippropelling apparatus that includes a simpler drivetrain system than inthe related art, guarantees stable counter-rotations of two propellers,and is easy to manufacture, install, maintain, and repair, and a shipincluding the same.

One or more embodiments of the present invention also provide a shippropelling apparatus including a sealing device for securing thereliability of sealing performance between a front propeller and a rearpropeller that rotate in counter-directions, and a ship including thesame.

One or more embodiments of the present invention also provide a shippropelling apparatus in which a bolt is inserted into a separationgroove of a front fixing member installed in the front of a gear box sothat the gear box may be efficiently separated from an installationspace in a tail of a ship due to a force applied to the gear box whenthe bolt is moved forward, and a ship including the same.

Technical Solution

One aspect of the present invention provides a ship propelling apparatusincluding a rotation shaft on which a rear propeller is fixed; a frontpropeller rotatably supported on the rotation shaft in front of the rearpropeller; and a counter-rotating device through which the rotationshaft passes, which includes a gear box including therein a plurality ofgears configured to reverse rotation of the rotation shaft and transferthe reversed rotation to the front propeller, and which is installed inan installation space formed at the rear of a ship. The rotation shaftincludes a measurement hole formed to pass through a center of therotation shaft for centering of the counter-rotating device installed inthe installation space; and an individual lubricant path separated fromthe measurement hole.

Also, the counter-rotating device may include a first connector coupledto a drive flange provided on the rotation shaft so as to transfer arotational force of the rotation shaft to the plurality of gears, and asecond connector coupled to a hub of the front propeller to transferoutputs of the plurality of gears to the front propeller.

Also, the plurality of gears may include a drive bevel gear coupled tothe first connector; a driven bevel gear supported rotatably around therotation shaft and coupled to the second connector; and at least onereverse bevel gear configured to reverse rotation of the drive bevelgear and transfer the reversed rotation to the driven bevel gear.

Another aspect of the present invention provides a ship propellingapparatus including a rear propeller fixed on a rotation shaft; a frontpropeller supported rotatably on the rotation shaft in front of the rearpropeller; and a counter-rotating device configured to reverse rotationof the rotation shaft and transfer the reversed rotation to the frontpropeller. The counter-rotating device may include a gear box includingtherein a plurality of gears for reversing rotation of the frontpropeller and accommodated in an installation space formed in a tail ofa ship, and a fixing flange provided at the front of the gear box, andincluding a separation groove which is a through-groove, wherein thegear box is separated from the installation space by applying a force tothe gear box by inserting a bolt into the separation groove.

Also, a plurality of separation grooves may be formed along a marginalportion of the fixing flange that is in close contact with the gear box.

The ship propelling apparatus may further include a coupling memberwhich is coupled to the separation groove and into which a clamp bolt isinserted to fix the front of the gear box on the tail of the ship.

Also, the gear box may be separated from the installation space due to aforce applied to the gear box by the bolt inserted into the separationgroove in a state in which the clamp bolt and the coupling member areloosened from the separation groove.

Also, a marginal portion of the fixing flange that is in close contactwith the gear box may include clamp grooves into which clamp bolts areinserted to fix a front cover on the tail of the ship; and separationgrooves formed alternately with the clamp grooves.

Also, the gear box may be separated from the installation space due to aforce applied to the front cover by the bolts inserted into theseparation grooves in a state in which the clamp bolts are loosened fromthe clamp grooves.

Also, the fixing flange may be coupled to the tail of the ship or formedintegrally with the tail of the ship.

Still another aspect of the present invention provides a ship propellingapparatus including a rear propeller fixed on a rotation shaft; a frontpropeller supported rotatably on the rotation shaft in front of the rearpropeller; a counter-rotating device including a plurality of gears forrevering rotation of the rotation shaft and transferring the reversedrotation to the front propeller, and accommodated in an installationspace formed in a tail of a ship; and a sealing device configured toseal between a hub of the front propeller and a hub of the rearpropeller. The sealing device may include a pressurizing ring membercoupled to one of the hubs and configured to apply a pressurizing forceto the other hub; and a support ring member coupled to the other hub,and configured to be in surface contact with the pressurizing ringmember in a sliding manner.

Also, the pressurizing ring member may include a fixing ring coupled toone of the hubs; a moving ring disposed apart from the fixing ring, andincluding a pressurizing unit that is in surface contact with thesupport ring member; and an elastic unit coupled between the fixing ringand the moving ring, and configured to apply a pressurizing force topressurize the moving ring toward the support ring member.

Also, the pressurizing unit may be coupled to the moving ring to bedetachable from the moving ring.

Also, a sliding surface of the pressurizing unit that is in surfacecontact with the support ring member may be perpendicular to therotation shaft.

Also, the elastic unit may include a pair of fixing units, both ends ofwhich are coupled to outer surfaces of the fixing ring and the movingring; and a circular arc unit configured to connect the pair of fixingunits to apply the pressurizing force.

The ship propelling apparatus may further include a sealing unitconfigured to seal between the moving ring and the pressurizing unit.

Advantageous Effects

A propelling apparatus according to an exemplary embodiment of thepresent invention is easy to manufacture and install, since centering ofa counter-rotating device can be performed via a measurement hole formedin a rotation shaft after a gear box of the counter-rotating device isloaded into an installation space formed in a tail of a ship in a statein which the counter-rotating device is manufactured and assembledoutside the ship.

Also, a propelling apparatus according to an exemplary embodiment of thepresent invention is easy to maintain and repair since a gear box of acounter-rotating device can be separated from a ship when the gear boxis out of order.

Also, a propelling apparatus according to an exemplary embodiment of thepresent invention causes a front propeller to reversely rotate using aplurality of bevel gears and thus may have a smaller volume and asimpler drivetrain system than a general planetary gear typecounter-rotating device. Also, since the volume of the counter-rotatingdevice is small, the counter-rotating device can be installed in a taila ship.

Also, in a propelling apparatus according to an exemplary embodiment ofthe present invention, a counter-rotating device may be installed in atail of a ship and thus a hollow shaft employed in the related art maybe omitted. Thus, the structure of a drivetrain system may be simplerthan in the related art, the size of an area that needs to be lubricatedmay be reduced, and various problems that may occur due to lubricationmay be minimized.

Also, in a propelling apparatus according to an exemplary embodiment ofthe present invention, a sealing device may allow radial displacement ofa front propeller or a rear propeller due to a non-uniform load appliedthereto, thereby enhancing the sealing performance thereof.

Also, a bolt may be inserted into a separation groove formed in a frontfixing member installed in the front of a gear box so that the gear boxmay be efficiently separated from an installation space in a tail of aship due to a force applied to the gear box when the bolt is movedforward.

DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a state in which a propellingapparatus is applied to a ship according to an exemplary embodiment ofthe present invention.

FIG. 2 is a cross-sectional view of a propelling apparatus according toan exemplary embodiment of the present invention.

FIG. 3 is an exploded perspective view of a propelling apparatusaccording to an exemplary embodiment of the present invention.

FIG. 4 is an exploded perspective view of a counter-rotating device of apropelling apparatus according to an exemplary embodiment of the presentinvention.

FIG. 5 is a detailed cross-sectional view of a structure in whichbearings are mounted to support a front propeller of a propellingapparatus according to an exemplary embodiment of the present invention.

FIG. 6 is a detailed cross-sectional view of a structure in whichbearings are mounted to support a front propeller of a propellingapparatus according to another exemplary embodiment of the presentinvention, in which a first radial bearing is loosened.

FIG. 7 is a cross-sectional view of a counter-rotating device of apropelling apparatus according to an exemplary embodiment of the presentinvention, in which a counter-rotating device is separated.

FIG. 8 is a cross-sectional view of a method of aligning a center of arotation shaft assembled in a gear box included in the counter-rotatingdevice of FIG. 7 and a center of a main drive shaft coupled to a drivesource using a shaft alignment tester.

FIG. 9 illustrates the shaft alignment tester of the FIG. 8.

FIG. 10 illustrates a state in which an optical sensor unit included inthe shaft alignment tester of FIG. 9 is installed and a rear end of arotation shaft is closed by a sealing cap.

FIG. 11 is a cross-sectional view of a state in which a counter-rotatingdevice of a propelling apparatus is mounted in an installation spaceformed in a tail of a ship according to an exemplary embodiment of thepresent invention.

FIG. 12 is a cross-sectional view of a first sealing device of apropelling apparatus according to an exemplary embodiment of the presentinvention.

FIG. 13 is an exploded perspective view of a first sealing device of apropelling apparatus according to an exemplary embodiment of the presentinvention.

FIG. 14 is a cross-sectional view of a second sealing device of apropelling apparatus according to an exemplary embodiment of the presentinvention.

FIG. 15 is a cross-sectional view of a propelling apparatus according toanother exemplary embodiment of the present invention.

FIG. 16 is a cross-sectional view of a sealing device installed betweenthe front of a propelling apparatus and a rear propeller according toanother exemplary embodiment of the present invention.

FIG. 17 illustrates a structure for supplying a lubricant to a sealingdevice installed between the front of a propelling apparatus and a rearpropeller according to another exemplary embodiment of the presentinvention.

FIG. 18 illustrates a structure of a connecting fluid path formed in ahub of a rear propeller of a propelling apparatus according to anotherexemplary embodiment of the present invention.

FIG. 19 is a diagram illustrating a change in the location of a fluidpath caused by a change in the length of a main shaft according toanother exemplary embodiment of the present invention.

FIG. 20 is a cross-sectional view of a separation groove formed in afront fixing member provided in front of a gear box included in thecounter-rotating device of FIG. 8.

FIG. 21 is a cross-sectional view of a fixing flange in which the frontfixing member of FIG. 20 is provided.

FIG. 22 is a cross-sectional view of a separation groove formed in thefixing flange of FIG. 21.

FIG. 23 is a cross-sectional view of a state in which a gear box isseparated from an installation space formed in a tail of a ship using ajack bolt inserted into the separation groove in the fixing flange ofFIG. 22.

FIG. 24 is a cross-sectional view of another example of the fixingflange of FIG. 22.

FIG. 25 is a cross-sectional view of another example of the fixingflange of FIG. 21 in which a coupling member is coupled to a separationgroove which also serves as a clamp groove.

FIG. 26 is a cross-sectional view of a state in which a gear box isseparated from an installation space formed in the tail of a ship by ajack bolt inserted into the separation groove in the fixing flange ofFIG. 25.

MODES OF THE INVENTION

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

As illustrated in FIGS. 1 and 2, a ship propelling apparatus accordingto an embodiment of the present invention includes a front propeller 10and a rear propeller 20 disposed at the rear of a ship 1 such that shaftlines thereof coincide with each other, and a counter-rotating device 30installed in a tail 3 of the ship 1 to cause the front propeller 10 andthe rear propeller 20 to rotate in opposite directions. That is, theship propelling apparatus is a double counter-rotating propellingapparatus in which the two propellers 10 and 20 rotate in oppositedirections to generate a propulsive force.

Here, the tail 3 of the ship 1 means a streamlined portion (i.e., astern boss) of the ship 1 protruding toward the rear thereof to installthe front and rear propellers 10 and 20 and the counter-rotating device30 therein. The tail 3 of the ship 1 may be manufactured by casting, andfixed on the ship 1 by welding. Also, the tail 3 of the ship 1 includesan installation space 4 having pass-through front and rear portions toaccommodate a gear box 40 of the counter-rotating device 30 which willbe described below. Inner surfaces of the installation space 4 may beprocessed in a cylindrical shape by boring to correspond to the shape ofthe gear box 40.

As illustrated in FIGS. 2 and 3, the counter-rotating device 30 includesthe gear box 40 accommodated in the installation space 4 of the tail 3of the ship 1, and a rotation shaft 5 supported rotatably on the gearbox 40 while passing through a roughly central portion of the gear box40.

As illustrated in FIGS. 2 to 4, the counter-rotating device 30 mayinclude a drive bevel gear 31 installed in the gear box 40 to rotatetogether with the rotation shaft 5, a driven bevel gear 32 disposedopposite the drive bevel gear 31 to be supported rotatably on therotation shaft 5 in the gear box 40, and a plurality of reverse bevelgears 33 configured to reverse rotation of the drive bevel gear 31 andtransfer the reversed rotation to the driven bevel gear 32. Thecounter-rotating device 30 may further include a cylindrical firstconnector 35 for connecting the rotation shaft 5 and the drive bevelgear 31, and a cylindrical second connector 36 for connecting the drivenbevel gear 32 and a hub 11 of the front propeller 10.

A front end of the rotation shaft 5 protruding toward the front of thegear box 40 may be connected to a main drive shaft 6 in the ship 1 suchthat the front end thereof can be combined with/separated from the maindrive shaft 6. The main drive shaft 6 may be connected to a drive source8 (a diesel engine, a motor, a turbine, etc.) installed in the ship 1 tocause the rotation shaft 5 to rotate together with the main drive shaft6 as illustrated in FIG. 1.

The rear propeller 20 is fixed on the rotation shaft 5 extending to therear of the gear box 40, and the front propeller 10 is rotatablysupported on an outer interface between the rear propeller 20 and thegear box 40. As will be described in detail below, the front propeller10 may be connected to the counter-rotating device 30 so that the frontpropeller 10 may rotate in a direction opposite to the rotationaldirection of the rear propeller 20 when the rotation shaft 5 rotates.

The main drive shaft 6 and the rotation shaft 5 may be coupled using acylindrical coupling device 7 by spline shaft coupling such that theycan be combined with each other or separated from each other. Here, thespline shaft coupling is provided as an example but a method ofconnecting the main drive shaft 6 and the rotation shaft 5 is notlimited thereto. Alternatively, flange coupling, a friction clutchmethod, a magnetic clutch method, etc. may be selectively employed.

The rear propeller 20 is fixed on a tail portion of the rotation shaft 5to rotate together with the rotation shaft 5 as illustrated in FIGS. 2and 3. The rear propeller 20 includes a hub 21 fixed on the rotationshaft 5, and a plurality of wings 22 provided on an outer surface of thehub 21. The hub 21 of the rear propeller 20 may be fixed on the rotationshaft 5 by press-fitting a shaft coupling hole 23 in a center thereof toan outer surface of the rotation shaft 5. A fixing cap 24 is clamped toa rear end of the rotation shaft 5 to firmly fix the rear propeller 20on the rotation shaft 5.

For the coupling, a tail portion 5 a of the rotation shaft 5 may beprovided in the form of a tapered outer surface, the external diameterof which tapers toward the rear thereof, and the shaft coupling hole 23of the hub 21 may be provided in the form of a tapered inner surfacecorresponding to the outer surface of the rotation shaft 5. In FIG. 2,reference numeral ‘25’ denotes a propeller cap installed on the hub 21to cover a rear end of the hub 21 of the rear propeller 20 and thefixing cap 24.

The front propeller 10 is installed rotatably on an outer surface of therotation shaft 5 between the rear propeller 20 and the counter-rotatingdevice 30. The front propeller 10 includes the hub 11 supportedrotatably on the outer surface of the rotation shaft 5, and a pluralityof wings 12 provided on an outer surface of the hub 11. The frontpropeller 10 may be installed on an outer surface of the rotation shaft5 before the rear propeller 20 is installed. Also, since the frontpropeller 10 rotates in a direction opposite to the rotational directionof the rear propeller 20, a wing angle of the front propeller 10 isdifferent from that of the rear propeller 20.

The hub 11 of the front propeller 10 may be supported rotatably on anouter surface of the rotation shaft 5 by a first thrust bearing 13, asecond thrust bearing 14, and a first radial bearing 15 as illustratedin FIGS. 2 and 5. The first thrust bearing 13 and the second thrustbearing 14 may be installed between a front inner side of the hub 11 andthe outer surface of the rotation shaft 5. The first radial bearing 15may be installed between a rear inner surface of the hub 11 and theouter surface of the rotation shaft 5.

The first radial bearing 15 may withstand a radial load applied by thefront propeller 10 in a radial direction of the rotation shaft 5, andthe first and second thrust bearings 13 and 14 may withstand thrustloads applied in front of and at the rear of the rotation shaft 5. Indetail, the second thrust bearing 14 may withstand a thrust load appliedfrom the front propeller 10 to a bow of the ship 1 when the ship 1 movesforward, and the first thrust bearing 13 may withstand a thrust loadapplied from the front propeller 10 toward the stern of the ship 1 whenthe ship 1 moves backward.

As illustrated in FIG. 5, an inner ring of the first thrust bearing 13and an inner ring of the second thrust bearing 14 are disposed incontact with each other in a state in which they are press-fitted at anouter surface of the rotation shaft 5, and may be thus supported not tobe pushed out in an axial direction. An outer ring of the first thrustbearing 13 is supported by a fixing ring 39 installed in the secondconnector 36 combined with the hub 11 not to be pushed out in the axialdirection.

A first cylindrical support ring 17 a and a second cylindrical supportring 17 b are installed between the hub 11 of the front propeller 10 andthe rotation shaft 5 not to push out the second thrust bearing 14 in theaxial direction. The first support ring 17 a may be disposed between anouter ring of the second thrust bearing 14 and an outer ring of thefirst radial bearing 15 to support the second thrust bearing 14 and thefirst radial bearing 15. The second support ring 17 b may be disposedbetween an inner ring of the second thrust bearing 14 and an inner ringof the first radial bearing 15 to support the second thrust bearing 14and the first radial bearing 15. Also, a distance adjustment ring 18 maybe installed on an inner surface of the hub 11 between the outer ring ofthe first radial bearing 15 and a first sealing cover 71 which will bedescribed below not to cause the outer ring of the first radial bearing15 to be pushed out in the axial direction. Here, in order to morestably support the outer ring of the first radial bearing 15, a case inwhich the distance adjustment ring 18 is installed is provided, but ifthe outer ring of the first radial bearing 15 is press-fitted on aninternal surface of the hub 11, the outer ring of the first radialbearing 15 may be fixed even when the distance adjustment ring 18 is notinstalled. Thus, the distance adjustment ring 18 may be selectivelyemployed according to design.

As illustrated in FIG. 5, a cylindrical wedge member 16 may be installedbetween the inner ring of the first radial bearing 15 and an outersurface of the rotation shaft 5 so that the inner ring of the firstradial bearing 15 may not be pushed out in the axial direction. Thewedge member 16 includes a tapered outer surface, the external diameterof which tapers toward the rear of the wedge member 16, and a screwthread formed on an outer surface of the rear of the wedge member 16. Aninner surface of the wedge member 16 may be press-fitted and fixed to anouter surface of the rotation shaft 5. The movement of the inner ring ofthe first radial bearing 15 may be constrained by inserting a lock nut16 a into the screw thread in the rear of the wedge member 16. Thus, thefirst radial bearing 15 may be firmly fixed between an outer surface ofthe rotation shaft 5 and an inner surface of the hub 11. A fixing clip16 b may be inserted into the wedge member 16 and the lock nut 16 a toprevent the wedge member 16 and the lock nut 16 a from being loosened.

When the front propeller 10 is installed, first, the first thrustbearing 13, the second thrust bearing 14, the first and second supportrings 17 a and 17 b, and the wedge member 16 may be sequentiallyinstalled on an outer surface of the rotation shaft 5. Then, asillustrated in FIG. 6, an outer side of the rotation shaft 5 is coupledto the hub 11 of the front propeller 10 to couple an inner surface ofthe hub 11 to the outer rings of the first and second thrust bearings 13and 14. Then, the first radial bearing 15 is installed by being pushedbetween an outer surface of the wedge member 16 and an inner surface ofthe hub 11, and then the lock nut 16 a may be inserted into the wedgemember 16 to fix the inner ring of the first radial bearing 15. Afterthe first radial bearing 15 is installed, the distance adjustment ring18 may be installed and the first sealing cover 71 may be mounted.

When the first radial bearing 15 is fixed using the wedge member 16 asdescribed above, even if an error occurs during manufacture ofcomponents, such as the first and second support rings 17 a and 17 b,etc. and an installation location of the first radial bearing 15 ischanged, a coupling error may be compensated by adjusting mountinglocations of the wedge member 16 and the first radial bearing 15. Thatis, the first radial bearing 15 may be fixed in a state in which thewedge member 16 and the first radial bearing 15 are pressed toward thefirst and second support rings 17 a and 17 b, thereby minimizing acoupling error between components. The distance between the outer ringof the first radial bearing 15 and the first sealing cover 71 may bemeasured and the distance adjustment ring 18 may be manufactured andinstalled based on the measured distance, in a state in which the firstradial bearing 15 is mounted.

When the front propeller 10 is separated from the rotation shaft 5 to berepaired in the future, the first sealing cover 71 and the distanceadjustment ring 18 are separated from each other, the lock nut 16 a isloosened from the wedge member 16 to separate the first radial bearing15, and then the front propeller 10 is pulled to be separated from therotation shaft 5 in a rear direction. After the front propeller 10 isseparated, the first and second thrust bearings 13 and 14, the wedgemember 16, are the first and second support rings 17 a and 17 b areexposed and thus may be also easily separated from the rotation shaft 5.

As illustrated in FIGS. 2 and 4, the gear box 40 of the counter-rotatingdevice 30 may include a body unit 41 having a cylindrical shape,configured to accommodate therein the drive bevel gear 31, the drivenbevel gear 32, and the plurality of reverse bevel gears 33, and bothends of which are open; a front cover 42 coupled to the body unit 41 toclose a front opening of the body unit 41; and a rear cover 43 coupledto the body unit 41 to close a rear opening of the body unit.

The front cover 42 may rotatably support the first connector 35 passingthrough a central portion thereof. The rear cover 43 may also rotatablysupport the second connector 36 passing through a central portionthereof. To this end, a front bearing 44 may be installed between anouter surface of the first connector 35 and the front cover 42, and arear outer bearing 45 may be installed between an outer surface of thesecond connector 36 and the rear cover 43.

A plurality of rear outer bearings 45 may be continuously installed in adirection of the length of the rotation shaft 5 to cause the secondconnector 36 to rotate while the second connector 36 are stablysupported. A rear inner bearing 46 may be installed between an innersurface of the second connector 36 and the rotation shaft 5 to rotatablysupport the second connector 36, and a cylindrical sleeve bearing 47 maybe installed between the first connector 35 and an outer surface of therotation shaft 5. Also, a cylindrical separation ring 49 may beinstalled on an outer surface of the rotation shaft 5 between an innerring of the rear inner bearing 46 and the sleeve bearing 47 to supportbetween the inner ring of the rear inner bearing 46 and the sleevebearing 47.

All the front bearing 44, the rear outer bearing 45, and the rear innerbearing 46 may be radial bearings. The bearings 44, 45, and 46 mayenable the rotation shaft 5, the first connector 35, and the secondconnector 36 to stably rotate while supporting radial load appliedthereto.

The drive bevel gear 31 is coupled to the first connector 35 by clampingthem with a plurality of clamp bolts 31 a to rotate together with thefirst connector 35. The driven bevel gear 32 is also coupled to thesecond connector 36 by clamping them with a plurality of clamp bolts 32a. An internal diameter of the driven bevel gear 32 may be spaced apartfrom the rotation shaft 5 so that rotation of the driven bevel gear 32may not be interfered by the rotation shaft 5.

The plurality of reverse bevel gears 33 are disposed between the drivebevel gear 31 and the driven bevel gear 32 while being engaged with thedrive bevel gear 31 and the driven bevel gear 32. A shaft 34 supportingthe reverse bevel gears 33 is disposed in a direction crossing therotation shaft 5 (a direction of the radius of the rotation shaft 5),and the reverse bevel gears 33 may be disposed around the rotation shaft5 in a radial form. Also, bearings 34 a and 34 b may be installed atboth ends of the shaft 34 of the reverse bevel gears 33 to smoothlyrotate the shaft 34.

An internal frame 50 may be installed in the gear box 40 to install thereverse bevel gears 33. The internal frame 50 may be fixed in the bodyunit 41 by clamping a plurality of fixing members 51 thereto while theinternal frame 50 is present in the gear box 40.

As illustrated in FIG. 4, a through-hole 52 through which the rotationshaft 5 passes is formed at a center of the internal frame 50, and theinternal frame 50 may be provided in a cylindrical or polygonal shape,the width W (in the direction of the length of the rotation shaft 5) ofwhich is less than a maximum external diameter of the reverse bevelgears 33.

The internal frame 50 accommodates the reverse bevel gears 33 to berotable, and includes a plurality of gear installation units 53, bothsides of which are open to cause the reverse bevel gears 33 to be gearedwith the drive bevel gear 31 and the driven bevel gear 32. The internalframe 50 further includes first shaft supports 54 and second shaftsupports 55 configured to support the bearings 34 a and 34 b installedat both ends of the shaft 34 of the reverse bevel gears 33,respectively. The components of the internal frame 50 may be disposedradially around the through-hole 52 so as to install the plurality ofreverse bevel gears 33.

As illustrated in FIG. 4, the first shaft support 54 and the secondshaft support 55 may be open in a direction of one side of the internalframe 50 so as to install the shaft 34 of the reverse bevel gears 33.Here, a first clamp member 54 a and a second clamp member 55 a may bemounted to fix the bearings 34 a and 34 b while covering the bearings 34a and 34 b. Thus, when the reverse bevel gears 33 are installed in theinternal frame 50, the reverse bevel gears 33, the shaft 34 of thereverse bevel gears 33, and the bearings 34 a and 34 b are assembledtogether, and the assembly is installed by loading it into the gearinstallation units 53 from a direction of one side surface of theinternal frame 50 and fixed by clamping the first and second clampmembers 54 a and 55 a thereto. The above method of installing thereverse bevel gears 33 into the internal frame 50 is just an example,and a method of installing the reverse bevel gear 33 is not limitedthereto. When the internal frame 50 is formed in a different shape thanthat described above, a method of installing the reverse bevel gears 33into the internal frame 50 may be changed.

The internal frame 50 into which the reverse bevel gears 33 areinstalled may be loaded into the body unit 41 of the gear box 40 andfixed in the body unit 41 by clamping the plurality of fixing members 51thereto, before the drive bevel gear 31, the driven bevel gear 32, thefront cover 42, and the rear cover 43 are installed during assembly ofthe counter-rotating device 30.

The plurality of fixing members 51 may be provided in the form ofcylindrical pins as illustrated in FIGS. 4 and 7. The fixing member 51is installed to be loaded into the body unit 41 while passing throughthe body unit 41 from an external side of the body unit 41. Thus, theinternal frame 50 may be supported to be fixed by inner ends of thefixing member 51. The internal frame 50 may be bound by inserting theinner ends of the fixing member 51 into the fixing grooves 56 formed inthe circumferential surface of the internal frame 50. Outer ends of thefixing member 51 may be fixed on the body unit 41 by clamping them witha clam screw.

In the gear box 40, a reverse bevel gear assembly including the internalframe 50 may be installed in the body unit 41, the drive bevel gear 31and the driven bevel gear 32 may be installed via openings at both sidesof the body unit 41, and then components such as the front cover 42, therear cover 43, the first connector 35, and the second connector 36 maybe installed. Thus, the counter-rotating device 30 is easy to assembleand repair.

In the present embodiment, the counter-rotating device 30 includes theplurality of reverse bevel gear 33 but may include one reverse bevelgear 33 provided that the reverse bevel gear 33 is capable of reversingrotation of the drive bevel gear 31 and transferring the reversedrotation to the driven bevel gear 32. A small-sized ship that does notrequire a high drive load may be actuated using only one reverse bevelgear.

Also, as illustrated in FIGS. 2 and 7, the counter-rotating device 30includes an electric power supply device 60 configured to connect therotation shaft 5 and the first connector 35 to be detachable from eachother. The electric power supply device 60 includes a drive flange 61provided on the rotation shaft 5 in front of the gear box 40, a drivenflange 62 provided on the first connector 35 to be disposed opposite thedrive flange 61, a friction member 63 disposed between the drive flange61 and the driven flange 62, and a plurality of connecting bolts 64 forclamping the drive flange 61, the driven flange 62, and the frictionmember 63 while passing through them. The drive flange 61 may beintegrally formed with the rotation shaft 5, or may be separatelymanufactured and fixed on the rotation shaft 5 by welding or the like.The driven flange 62 may be integrally formed with the first connector35. The friction member 63 may be split into a plurality ofsemi-circulator parts so that the friction member 63 may be removed inan outer radial direction by loosening and removing the connecting bolts64.

The electric power supply device 60 may be configured such that theplurality of connecting bolts 64 are loosened to separate the frictionmember 63 from the electric power supply device 60 to stop supply ofpower to the drive flange 61 and the driven flange 62 if needed. Forexample, when the counter-rotating device 30 malfunctions during anoperation of the ship 1, supply of power to the first connector 35 fromthe rotation shaft 5 may be stopped. In this case, the ship 1 may beoperated only by operating the rear propeller 20.

The second connector 36 includes a connecting flange 37 coupled to thehub 11 of the front propeller 10 at a read end thereof. The connectingflange 37 may be integrally formed with the second connector 36, andfixed on a front surface of the hub 11 of the front propeller 10 byclamping them with a plurality of clamp bolts 37 a. Thus, rotation ofthe driven bevel gear 32 may be transferred to the front propeller 10via the second connector 36.

A cylindrical third support ring 38 a and a cylindrical fourth supportring 38 b supporting the rear inner bearing 46 may be installed betweenthe second connector 36 and an outer surface of the rotation shaft 5.The third support ring 38 a may be disposed between an inner ring of therear inner bearing 46 and an inner ring of the first thrust bearing 13to maintain the distance between the inner ring of the rear innerbearing 46 and the inner ring of the first thrust bearing 13. The fourthsupport ring 38 b may be installed on an inner surface of the secondconnector 36 to support an outer ring of the rear inner bearing 46.Also, the fixing ring 39 may be mounted at a rear end of the secondconnector 36 to prevent the fourth support ring 38 b from beingseparated. The fixing ring 39 may support the outer ring of the firstthrust bearing 13 as illustrated in FIGS. 2 and 5.

In the counter-rotating device 30, the first connector 35 rotates whenthe rotation shaft 5 rotates, and the drive bevel gear 31 coupled to thefirst connector 35 also rotates. The rotation of the drive bevel gear 31is reversed by the plurality of reverse bevel gears 33 and transferredto the driven bevel gear 32. Thus, the driven bevel gear 32 rotates in adirection opposite to the rotational direction of the drive bevel gear31. Also, the rotation of the driven bevel gear 32 is transferred to thefront propeller 10 via the second connector 36. Thus, the frontpropeller 10 and the rear propeller 20 may rotate in oppositedirections.

As described above, the counter-rotating device 30 according to thepresent invention causes the two propellers 10 and 20 to rotate inopposite directions using the plurality of bevel gears 31, 32, and 33,and may be thus smaller in volume than a general planetary gear typecounter-rotating device according to the related art. Accordingly, thevolume of the gear box 40 installed in the tail 3 of the ship 1 may beminimized.

A general planetary gear type counter-rotating device includes a sungear installed on a rotation shaft, a planet gear installed at an outerside of the sun gear, and a cylindrical internal gear installed at anouter side of the planet gear, and thus has a relatively large volume.Also, the volume of the general planetary gear type counter-rotatingdevice should be very large in consideration of rotation of the internalgear which is an outermost gear and an outer casing thereof. Thus, thegeneral planetary gear type counter-rotating device is actually verydifficult to install in a tail of a ship. Even if the general planetarygear type counter-rotating device is installed in the tail of the ship,the tail of the ship should be very large.

As illustrated in FIG. 2, a propelling apparatus according to thepresent embodiment includes a first sealing device 90 for sealing aspace between the tail 3 of the ship 1 and the hub 11 of the frontpropeller 10 to protect them against seawater (or fresh water) orforeign substances, and a second sealing device 110 for sealing a spacebetween the hub 11 of the front propeller 10 and the hub 21 of the rearpropeller 20 for the same purpose.

As illustrated in FIG. 12, the first sealing device 90 may include acylindrical first lining 91 installed on the connecting flange 37 of thesecond connector 36 fixed on the front surface of the hub 11 of thefront propeller, and a cylindrical first sealing member 92 covering anouter surface of the first lining 91 in contact with an outer surface ofthe first lining 91 and one end of which is fixed on the rear cover 43.

The first sealing member 92 includes a plurality of packings 93 a, 93 b,and 93 c installed on an inner surface thereof facing the first lining91 to be spaced apart from one another in contact with an outer surfaceof the first lining 91, and a fluid path 95 via which a fluid issupplied to seal grooves between the packings 93 a, 93 b, and 93 c. Thefluid path 95 of the first sealing member 92 may be connected to alubricant supply path 96 passing through the front of the gear box 40and the rear covers 42 and 43 so as to supply a lubricant of apredetermined pressure to the front of the gear box 40 and the rearcovers 42 and 43 (see FIG. 2). The packings 93 a, 93 b, and 93 c arepressurized against the first lining 91 by supplying the lubricant ofthe predetermined pressure to the grooves between the packings 93 a, 93b, and 93 c, thereby preventing seawater or foreign substances frompenetrating into the ship 1.

The first lining 91 may be split into a first member 91 a and a secondmember 91 b, both sides of which have semi-circular shape as illustratedin FIG. 13. A packing 91 d may be inserted into split portions 91 c ofthe first and second members 91 a and 91 b to seal the first and secondmembers 91 a and 91 b when the first and second members 91 a and 91 bare combined with each other. A first binding unit 91 e protruding froma side to another side is provided at a free end of a split portion ofthe first member 91 a. A second binding unit 91 f corresponding to thefirst binding unit 91 e is provided at the second member 91 b oppositeto the first member 91 a to be combined with the first binding unit 91e. Here, a clamp bolt 91 g may be clamped to the first binding unit 91 eand the second binding unit 91 f to firmly couple them with each other.A flange unit 91 h fixed on the connecting flange 37 may be firmly fixedon the hub 11 by clamping the flange unit 91 h with a plurality of clampbolts 91 i. Although both ends of the first lining 91 are split to beeasily installed, the first lining 91 is not limited thereto and mayhave a cylindrical shape in which the first member 91 a and the secondmember 91 b are integrally formed.

Similarly, the first sealing member 92 may be manufactured by stackingand fixing rings 92 a, 92 b, and 92 c, which are formed in a semicircleshape, on an outer side of the first lining 91 in the direction of thelength of the rotation shaft 5. The rings 92 a, 92 b, and 92 c may bebound to one another by clamping them with bolts or welding.

As illustrated in FIG. 14, the second sealing device 110 may include acylindrical second lining 111 installed on a front surface of the hub 21of the rear propeller 20, and a cylindrical second sealing member 112covering an outer surface of the second lining 111 in contact with theouter surface of the second lining 111 and one end of which is fixed ona rear end of the hub 11 of the front propeller. Similar to the firstsealing member 92, the second sealing member 112 includes a plurality ofpackings 113 a, 113 b, and 113 c installed therein, and a fluid path 115via which a fluid is supplied to grooves between the packings 113 a, 113b, and 113 c.

The fluid path 115 of the second sealing member 112 may communicate witha lubricant path 120 provided on a location biased from a centralportion of the rotation shaft 5. To this end, a first connecting fluidpath 121 connecting the lubricant path 120 and an inner space 122 of thesecond lining 111 may be formed in the rotation shaft 5 in the directionof the radius of the rotation shaft 5, and a second connecting fluidpath 123 communicating between the inner space 122 of the second lining111 and the fluid path 115 of the second sealing member 112 may beformed in the hub 11 of the front propeller 10. Thus, the packings 113a, 113 b, and 113 c may be pressurized by a lubricant supplied towardthe second sealing member 112 from the lubricant path 120, therebysealing the packings 113 a, 113 b, and 113 c.

A measurement through-hole 100 is formed in a central portion of therotation shaft 5 in the axial direction to control centering of the gearbox 40 when the gear box 40 is installed in the installation space 4 asillustrated in FIG. 2. The centering of the gear box 40 performed viathe measurement through-hole 100 will be described below.

Similar to the first lining 91 and the first sealing member 92 of thefirst sealing device 90, the second lining 111 and the second sealingmember 112 are formed in a semicircle shape and combined with each otherafter the rear propeller 20 is installed.

Although the lubricant path 120 is disposed as an independent fluid pathon the location biased from the central portion of the rotation shaft 5in the present embodiment, embodiments of the present invention are notlimited thereto and a plurality of lubricant paths 120 may be disposedin a radial form around the central portion of the rotation shaft 5.Also, the lubricant path 120 may serve as lubricant supply path viawhich a lubricant is supplied from a lubricant supply device (not shown)installed in the ship 1, may lubricate the vicinity of the rotationshaft 5, or serve as a lubricant collecting path via which a lubricantsupplied to a sealing device is collected to the lubricant supplydevice.

As illustrated in FIGS. 2 and 5, the front propeller 10 includes thering type first sealing cover 71 mounted at the rear end of the hub 11to seal a space between an outer surface of the rotation shaft 5 and aninner surface of the hub 11. The first sealing cover 71 includes asealing member 71 a for increasing an adhesion between an innercircumferential surface of the first sealing cover 71 and the outersurface of the rotation shaft 5. The first sealing cover 71 may preventseawater from flowing into the gear box 40 even when the seawaterpenetrates into the inner space 122 of the second lining 111 due to amalfunction of the second sealing device 110. That is, the first sealingcover 71 may serve as a secondary barrier wall to more reliably preventseawater from penetrating into the gear box 40.

Referring to FIG. 2, a second sealing cover 72 having a similar shape asthat of the first sealing cover 71 may be installed on the driven flange62 in front of the gear box 40 to seal between the driven flange 62 andan outer surface of the rotation shaft 5. The second sealing cover 72may prevent a lubricant filled in the gear box 40 from leaking to theship 1.

The counter-rotating device 30 may include a front-surface sealing cover73 for covering a front surface of the front bearing 44 between thefront cover 42 and the first connector 35 to seal the front bearing 44,and a rear-end sealing cover 74 for covering a rear end of the rearouter bearing 45 between the rear cover 43 and the second connector 36to seal the rear outer bearing 45. The front-surface sealing cover 73and the rear-end sealing cover 74 may be provided in a form similar asthat of the first sealing cover 71 described above.

The front-surface sealing cover 73 and the rear-end sealing cover 74 mayprevent a lubricant in the gear box 40 from leaking to the outside ofthe gear box 40. Furthermore, even if seawater penetrates into an innerspace of the first lining 91 due to a malfunction of the first sealingdevice 90, the rear-end sealing cover 74 may serve as a secondarybarrier wall preventing the seawater from flowing into the gear box 40,similar to the first sealing cover 71.

Also, a propelling apparatus according to the present embodiment mayinclude a second radial bearing 81, a third thrust bearing 82, and afourth thrust bearing 83 which support the rotation shaft 5 in front ofthe gear box 40. The second radial bearing 81 may be fixed on a firstbearing support 86 in the ship 1 while being accommodated in a firstbearing case 84. The third and fourth thrust bearings 82 and 83 may bealso fixed on a second bearing support 87 in the ship 1 such that innerrings thereof are supported while being accommodated in a second bearingcase 85.

The second radial bearing 81 supports the rotation shaft 5 in front ofthe gear box 40, thereby preventing the rotation shaft 5 from vibratingor shaking in a radial direction thereof. The third and fourth thrustbearings 82 and 83 transfer an axial-direction force, which istransferred to the rotation shaft 5 from the front and rear propellers10 and 20, toward the ship 1. In particular, the third thrust bearing 82transfers to the ship 1 a force applied from the rotation shaft 5 to thebow of the ship 1 when the ship 1 moves forward, and the fourth thrustbearing 83 transfers to the ship 1 a force applied from the rotationshaft 5 to the tail of the ship 1 when the ship 1 moves backward.

In FIG. 2, reference numeral ‘131’ denotes a first cover ring forcovering a space between the tail 3 of the ship 1 and the hub 11 of thefront propeller 10 at an outer side of the first sealing device 90, andreference numeral ‘132’ denotes a second cover ring for covering a spacebetween the hub 11 of the front propeller 10 and the hub 21 of the rearpropeller 20 at an outer side of the second sealing device 110. Thefirst cover ring 131 may be fixed on the tail 3 of the ship 1 to beslightly spaced from the hub 11 of the front propeller 10 or may befixed on hub 11 of the front propeller 10 to be slightly spaced from thetail 3 of the ship 1 so that the first cover ring 131 may rotatetogether with the front propeller 10. Similarly, the second cover ring132 may be fixed on the hub 11 of the front propeller 10 or the hub 21of the rear propeller 20, and rotate together with the front propeller10 or the rear propeller 20 on which the second cover ring 132 is fixed.

Next, a method of manufacturing a propelling apparatus according to thepresent embodiment and installing the propelling apparatus in a shipwill be described with reference to FIGS. 7 to 11 below.

As illustrated in FIG. 7, in order to install a propelling apparatus,the gear box 40 of the counter-rotating device 30, components related tothe gear box 40, and the rotation shaft 5 are assembled together beforethe propelling apparatus is installed in the ship 1. That is, the bodyunit 41, the internal frame 50 in which the reverse bevel gears 33 areassembled, the drive bevel gear 31, the driven bevel gear 32, the firstconnector 35, the front cover 42, the front bearing 44, the secondconnector 36, the rear cover 43, the rear outer bearing 45, etc. areassembled together at an outer side of the rotation shaft 5. The firstlining 91 and the first sealing member 92 of first sealing device 90 arealso installed between the connecting flange 37 of the second connector36 and the rear cover 43.

The counter-rotating device 30 may be precisely manufactured sincecomponents thereof may be manufactured and then assembled in a separatemanufacturing plant. Also, the first sealing device 90 that should begenerally installed after the front propeller 10 is installed may bemounted beforehand in the counter-rotating device 30, therebysimplifying a subsequent process of installing the propelling apparatusin the ship 1.

The rotation shaft 5 and the counter-rotating device 30 assembled in themanufacturing plant may be transferred to a dock where the ship 1 ismanufactured or the like using a transportation means, and installed inthe tail 3 of the ship 1. In this case, a lifting device, e.g., a crane,which is capable of lifting the assembly of the counter-rotating device30 may be used. When the counter-rotating device 30 is mounted, first,the gear box 40 of the counter-rotating device 30 is loaded into theinstallation space 4 in the tail 3 of the ship 1 from the rear of theship 1 in a sliding manner.

Then, the rotation shaft 5 and the main drive shaft 6 are aligned toeach other such that the centers thereof coincide. That is, the maindrive shaft 6 is connected to the drive source 8 such that the center ofthe main drive shaft 6 coincides with a (virtual) shaft line of thedrive source 8. Thus, since the rotation shaft 5 is aligned such thatthe center thereof coincides with the center of the main drive shaft 6,the center of the rotation shaft 5 and the center of the main driveshaft 6 coincide with each other.

Referring to FIG. 8, a shaft alignment tester may be used to align therotation shaft 5 and the main drive shaft 6 with each other such thatthe centers thereof coincide with each other.

In the shaft alignment tester, light is radiated to the measurementthrough-hole 100 of the rotation shaft 5 from the front of the rotationshaft 5 using a light radiation unit 210 (which will be describedbelow), and a point on which the light passing through the measurementthrough-hole 100 of the rotation shaft 5 is incident is measured usingan optical sensor unit 220 (which will be described below). Examples ofthe radiated light may include a laser ray, infrared light, etc.

The rotation shaft 5 is aligned with the main drive shaft 6 and coupledto the main drive shaft 6, based on a value measured by the shaftalignment tester. In this case, the front end of the rotation shaft 5 iscoupled to the main drive shaft 6 to be detachable from the main driveshaft 6 as described above. Also, the main drive shaft 6 and therotation shaft 5 may be coupled to each other, for example, by thecylindrical coupling device 7 by spline shaft coupling such that theycan be separated from/coupled to each other.

Referring to FIG. 9, the shaft alignment tester includes the lightradiation unit 210 and the optical sensor unit 220.

As illustrated in FIG. 9( a), the light radiation unit 210 radiateslight to measurement through-hole 100 of the rotation shaft 5 from thecenter of the main drive shaft 6. The light radiation unit 210 may beinstalled at an inner side of the main drive shaft 6 or in front of thedrive source 8 to be installed at an inner side of a tunnel bearing 9(see FIG. 1) supporting the main drive shaft 6. Hereinafter, a case inwhich the light radiation unit 210 is installed at the inner side of themain drive shaft 6 will be described for convenience of explanation.Here, the tunnel bearing 9 is designed such that the center thereofcoincides with the center of the main drive shaft 6 with respect to ashaft line, and may include, for example, a sleeve bearing.

The light radiation unit 210 includes a light source 211 and a firsttiltmeter 212. The light source 211 radiates light. In this case, thelight may be a laser ray, etc. The light source 211 radiates light in ahorizontal direction that coincides with the center of the main driveshaft 6. In this case, the first tiltmeter 212 measures horizontality ofa light radiation unit 210. By measuring the horizontality of the lightradiation unit 210, whether the light is radiated from the lightradiation unit 210 in the horizontal direction may be tested.

The height of the light radiation unit 210 may be adjusted using a firstadjustment member 213 to control a reference position C1 at which lightis to be radiated to coincide with the center of the main drive shaft 6.The reason why the height of the light radiation unit 210 is adjusted isto set the reference position C1 at which light is radiated to coincidewith the center of the main drive shaft 6, so that light may be radiatedonto a point that coincides with the center of the main drive shaft 6.

The first adjustment member 213 includes a first support bar 213 a and afirst leveler 213 b. The height of the light radiation unit 210 may beadjusted by moving the light radiation unit 210 vertically along thefirst support bar 213 a using the first leveler 213 b. An operator mayadjust the height of the light radiation unit 210 using an externaldevice connected to the light radiation unit 210 while checking thecoordinates of the reference position C1 of the light radiation unit210, so that the reference position C1 of the light radiation unit 210may coincide with the center of the main drive shaft 6.

The first support bar 213 a is coupled to a first fixing unit 215. Thelight radiation unit 210 is fixed on an inner surface of the main driveshaft 6 using the first fixing unit 215. For example, since the bottomof the first fixing unit 215 is formed to correspond to an internalcurvature of the main drive shaft 6, the first fixing unit 215 may thusenable the light radiation unit 210 to be stably fixed on the innersurface of the main drive shaft 6. The first fixing unit 215 may beformed of a magnetic substance, and thus enables the light radiationunit 210 to be installed to be attachable/detachable. However,embodiments of the present invention are not limited thereto, and thefirst fixing unit 215 may be attached by welding or the like.

As illustrated in FIG. 9( b), the optical sensor unit 220 is installedat the rotation shaft 5 or the rear of the rotation shaft 5 to face thelight radiation unit 210, and measures a point on which light isincident. For example, the optical sensor unit 220 may be installed in ahollow portion of or a rear end 5 b of the rotation shaft 5 to measure apoint on which light is incident. The optical sensor unit 220 includes alight-receiving unit 221, a second tiltmeter 222, and a determinationunit (not shown).

The light-receiving unit 221 detects the light incident from the lightradiation unit 210. The light-receiving unit 221 may display the pointon which light is incident on a screen thereof. An operator may checkthe point on which light is incident, which is displayed on the screen,and align the gear box 40 such that the center of the rotation shaft 5and the center of the main drive shaft 6 coincide with each other. Inthis case, as another example, data regarding the coordinates of pointon which light is incident may be transmitted to an external device. Inthis case, the operator may check a state in which the rotation shaft 5and the main drive shaft 6 are aligned to each other, based on thecoordinates displayed on the external device.

The second tiltmeter 222 measures the horizontality of the opticalsensor unit 220, so that the light radiation unit 210 and the opticalsensor unit 220 may radiate light and receive the light in thehorizontal direction.

The determination unit determines whether the center of the rotationshaft 5 and the center of the main drive shaft 6 are aligned to eachother, based on the point on which light is incident. The determinationunit determines that the center of the rotation shaft 5 and the centerof the main drive shaft 6 are aligned to each other when light isincident on a reference position C2 of the optical sensor unit 220 thatcoincides with the reference position C1 of the light radiation unit 210radiating light. Here, the reference position C2 of the optical sensorunit 220 is set to coincide with the center of the rotation shaft 5.When it is determined that the center of the rotation shaft 5 and thecenter of the main drive shaft 6 are aligned to each other, this factmay be informed to the operator using an alarm, etc.

The height of the optical sensor unit 220 may be adjusted by a secondadjustment member 223 such that the reference position C2 on which lightis incident coincides with the center of the rotation shaft 5. Thesecond adjustment member 223 includes a second support bar 223 a and asecond leveler 223 b. The height of the optical sensor unit 220 may beadjusted by moving the optical sensor unit 220 vertically along thesecond support bar 223 a using the second leveler 223 b. An operator mayadjust the height of the optical sensor unit 220 using an externaldevice connected to the optical sensor unit 220 while checking thecoordinates of the reference position C2 of the optical sensor unit 220,so that the reference position C2 of the optical sensor unit 220 maycoincide with the center of the rotation shaft 5.

The second support bar 223 a is coupled to a second fixing unit 225. Theoptical sensor unit 220 is fixed on a rear end surface of the rotationshaft 5 using the second fixing unit 225. The second fixing unit 225 maybe formed of a magnetic substance and thus enables the optical sensorunit 220 to be installed to be attachable/detachable. However,embodiments of the present invention is not limited thereto and thesecond fixing unit 225 may be attached by welding, using a clamp means,etc.

When it seems that the shafts 5 and 6 are misaligned to each other, theshaft alignment tester may measure an alignment state between the shafts5 and 6 by radiating and receiving light periodically or according to acontrol command received from an external device, and provide a resultof the measurement to the external device. To this end, the lightradiation unit 210 and the optical sensor unit 220 may each include acontroller (not shown). For example, the controller of the lightradiation unit 210 causes the light radiation unit 210 to radiate lightperiodically or according to a control command transmitted from theexternal device, and the controller of the optical sensor unit 220measures a point on which the received light is incident and provides aresult of the measurement to the external device.

FIG. 10( a) illustrates a structure in which the optical sensor unit 220is fixed at the rear end of the rotation shaft 5. Referring to FIG. 10(b), when measurement using the shaft alignment tester is completed, therear end of the rotation shaft 5 is closed by a sealing cap 230.

As described above, since the rotation shaft 5 and the main drive shaft6 are aligned with each other using the shaft alignment tester such thatthe centers thereof coincide with each other, the precision andefficiency of aligning the shafts 5 and 6 may be increased and theshafts 5 and 6 may be prevented from being fatigued, damaged, andvibrating.

After the counter-rotating device 30 is loaded and arranged in theinstallation space 4 of the tail 3 of the ship 1, a front fixing member48 a and a rear fixing member 48 b are respectively installed on thefront and rear of the gear box 40 to fix the gear box 40 in the tail 3of the ship 1 as illustrated in FIG. 11. The front and rear fixingmembers 48 a and 48 b may be split into several parts. The front andrear fixing members 48 a and 48 b may be fixed on a structure includingthe gear box 40 and the tail 3 of the ship 1 by clamping them with aplurality of clamp bolts.

An operator may exactly install the rear fixing member 48 b by accessingthe rear of the ship 1, and the front fixing member 48 a by accessingthe inside of the ship 1. As described above, the counter-rotatingdevice 30 installed by being loaded in the installation space 4 of thetail 3 of the ship 1 may be separated from the ship 1 and repaired whenthe counter-rotating device 30 malfunctions. Accordingly, thecounter-rotating device 30 is easy to repair.

In the present embodiment, the front fixing member 48 a and the rearfixing member 48 b are clamped to the front and rear of the gear box 40in order to firmly fix the gear box 40. However, when the gear box 40 isloaded in the installation space 4, an outer surface of the gear box 40is continuously supported by an inner surface of the installation space4 and thus the gear box 40 may be fixed in the tail 3 of the ship 1 byclamping only the rear fixing member 48 b thereto.

After the gear box 40 is fixed in the tail 3 of the ship 1, the maindrive shaft 6 and the rotation shaft 5 are coupled by the couplingdevice 7, and the second radial bearing 81 and the third and fourththrust bearings 82 and 83 are installed in the ship 1 to support therotation shaft 5 in the ship 1.

After the counter-rotating device 30 is installed in the tail 3 of theship 1, the front propeller 10 and the rear propeller 20 and othercomponents related thereto may be installed on the rotation shaft 5, andthe second sealing device 110 may be installed as illustrated in FIGS. 1and 2, thereby completing installation of the propelling apparatus.

As described above, the gear box 40 mounted in the installation space 4of the tail 3 of the ship 1 may malfunction and should be thus separatedfrom the installation space 4 to be repaired. However, the gear box 40weighs at least several tens of tons and is thus difficult to beseparated from installation space 4. Thus, there is a growing need toefficiently separate the gear box 40 from the installation space 4.

To this end, referring to FIG. 20, the front fixing member 48 a mayinclude a first clamp groove 2201, a second clamp groove 2202, and aseparation groove 2211. The front fixing member 48 a is fixed on thetail 3 of the ship 1 by screwing a clamp bolt 2208 into the first clampgroove 2201. Also, the gear box 40 is fixed on the tail 3 of the ship 1by screwing a clamp bolt 2209 into the second clamp groove 2202. In thiscase, when the gear box 40 is loaded in the installation space 4, anouter surface of the gear box 40 is continuously supported by an innersurface of the installation space 4 and thus the gear box 40 may be thusfixed on the tail 3 of the ship 1 by simply clamping only the rearfixing member 48 b thereto. In this case, the second clamp groove 2202and the clamp bolt 2209 clamped thereto may be omitted.

In order to separate the gear box 40 from the installation space 4, theclamp bolt 2209 is loosened from the rear fixing member 48 b (see FIG.8) while the front fixing member 48 a is coupled to the tail 3 of theship 1. Then, when a jack bolt 2212 which will be described below isscrewed into the separation groove 2211 and moved forward to apply aforce to the front cover 42, the gear box 40 is separated from theinstallation space 4. Here, that the gear box 40 is separated from theinstallation space 4 by screwing the jack bolt 2212 into the separationgroove 2211 may be understood to include moving the gear box 40 to bespaced by a predetermine distance from the installation space 4 byscrewing the jack bolt 2212 into the separation groove 2211.

Referring to FIG. 21, the front fixing member 48 a may be provided inthe form of a fixing flange 2210. Similar to the front fixing member 48a, the separation groove 2211 which is a through-groove is formed in thefixing flange 2210 in front of the gear box 40 to separate the gear box40 from the installation space 4 when a force is applied to the gear box40 by screwing a bolt into the separation groove 2211. In this case, thefixing flange 2210 may be coupled to the tail 3 of the ship 1 by weldingor clamping them with a bolt or may be integrally formed with the tail 3of the ship 1.

Referring to FIGS. 22 and 23, a plurality of separation grooves 2211 maybe formed along a marginal portion 2213 of the fixing flange 2210 whichis closely in contact with the front cover 42 of the gear box 40. Thegear box 40 may be separated from the installation space 4 by screwingthe jack bolt 2212 into each of the separation grooves 2211 formed alongthe marginal portion 2213 of the fixing flange 2210 and moving the jackbolt 2212 by applying a force to the front cover 42 in a state in whichthe rear fixing member 48 b (see FIG. 8) is unclamped from the gear box40. In the present embodiment, a case in which the jack bolt 2212 isused has been described above, but embodiments of the present inventionare not limited thereto and various other clamp means may be usedprovided that they can be used to apply a force to the front cover 42clamped into the separation groove 2211 in order to separate the gearbox 40 from the installation space 4.

Referring to FIG. 24, as another example, the fixing flange 2210 may beprovided in a form including the clamp grooves 2202 and separationgrooves 2211 as describe above. That is, the marginal portion 2213 ofthe fixing flange 2210 may include the clamp grooves 2202 which arethrough-grooves into which clamp bolts (not shown) are screwed in orderto fix the gear box 40 on the tail 3 of the ship 1. In this case, theseparation grooves 2211 and the clamp grooves 2202 may be alternatelyformed.

In this case, in order to separate the gear box 40 from the installationspace 4, the rear fixing member 48 b (see FIG. 8) is unclamped and theclamp bolts are unscrewed from the clamp grooves 2202. Next, the jackbolt 2212 is screwed in each of the separation grooves 2211 formed inthe marginal portion 2213 of the fixing flange 2210 and moved forward byapplying a force to the front cover 42 to separate the gear box 40 fromthe installation space 4.

The structure of the marginal portion 2213 of the fixing flange 2210described above with reference to FIGS. 22 and 24 is also applicable toa marginal portion of the front fixing member 48 a of FIG. 20 that isclosely in contact with the front cover 42 of the gear box 40.

Referring to FIGS. 25 and 26, the separation groove 2211 of FIG. 22 mayalso serve as a clamp groove into which a clamp bolt 2209 a is insertedto fix the gear box 40 on the tail 3 of the ship 1. In this case, it isassumed that the diameter of the jack bolt 2212 is greater than that ofthe clamp bolt 2209 a.

To this end, a coupling member 2220 including a screw thread in innerand outer marginal portions thereof may be coupled to the separationgroove 2211. The coupling member 2220 includes a hollow portion 2220 ainto which the clamp bolt 2209 a is inserted to fix the front of thegear box 40 on the tail 3 of the ship 1. An inner shape of theseparation groove 2211 corresponds to a shape of the coupling member2220. The clamp bolt 2209 a may be formed in a shape including a screwthread corresponding to an inner shape coupling member 2220.

To fix the gear box 40 on the tail 3 of the ship 1, the coupling member2220 is coupled to the separation groove 2211, and the clamp bolt 2209 ais inserted into the coupling member 2220 to couple the coupling member2220 to a groove 42 a formed in a front surface of the front cover 42 ofthe gear box 40. Then, in order to separate the gear box 40 from theinstallation space 4, the rear fixing member 48 b (see FIG. 8) isunclamped, the clamp bolt 2209 a and the coupling member 2220 aresequentially loosened from the separation groove 2211, and the jack bolt2212 is inserted into the separation groove 2211 and moved forward toapply a force to the gear box 40. In this case, the jack bolt 2212 maybe formed in a shape corresponding to the inner shape of the separationgroove 2211 so that the jack bolt 2212 may be inserted into theseparation groove 2211.

Next, an operation of a propelling apparatus according to the presentinvention will be described.

In the propelling apparatus, when the rotation shaft 5 rotates as thedrive source 8 included in the ship 1 operates, the rear propeller 20coupled directly to the rear end of the rotation shaft 5 rotatestogether with the rotation shaft 5 in a direction in which the rotationshaft 5 rotates. At the same time, the drive bevel gear 31 of thecounter-rotating device 30 rotates together with the rotation shaft 5since it is fixed on the rotation shaft 5. The rotation of the drivebevel gear 31 is reversed by the plurality of reverse bevel gears 33 andtransferred to the driven bevel gear 32. Thus, the driven bevel gear 32rotates in a direction opposite to the rotational direction of therotation shaft 5. Thus, the front propeller 10 coupled to the drivenbevel gear 32 via the second connector 36 rotates in a directionopposite to the rotational direction of the rear propeller 20.

The front propeller 10 and the rear propeller 20 that rotate in oppositedirections have different wing angles and thus generate propelling waterflows in the same direction. That is, the front propeller 10 and therear propeller 20 generate propelling water flows in a backwarddirection when the ship 1 moves forward, and generate propelling waterflows in a forward direction while rotating reversely when the shipmoves backward. Propelling water flows generated when the ship 1 movesforward collect as a propulsive force the rotational energy of a liquidpassing through the front propeller 10 when the rear propeller 20rotates reversely, thereby improving the propelling performance of theship 1. This also applies when the ship 1 moves backward.

When the ship 1 moves forward, the front propeller 10 generatespropelling water flows in the backward direction and thus a reactionforce corresponding the propelling water flows is applied to the frontpropeller 10. The reaction force is transferred to the rotation shaft 5via the second thrust bearing 14 and used as a propulsive force. Whenthe ship 1 moves forward, the rear propeller 20 also generatespropelling water flows in the backward direction and a reaction force isapplied thereto. The reaction force is also transferred to the rotationshaft 5 directly coupled to the rear propeller 20 and used as apropulsive force.

When the ship 1 moves backward, a propulsive force generated by thefront propeller 10 is transferred to the rotation shaft 5 via the firstthrust bearing 13, and a propulsive force generated by the rearpropeller 20 is transferred to the rotation shaft 5 coupled directly tothe rear propeller 20.

Accordingly, in the propelling apparatus according to the presentembodiment, propulsive forces generated by operating the front propeller10 and the rear propeller 20 are transferred to the rotation shaft 5when the ship 1 moves forward and backward. The propulsive forcestransferred to the rotation shaft 5 are transferred to the ship 1 viathe third and fourth thrust bearings 82 and 83, thereby propelling theship 1 to move.

A sealing device installed between a front propeller and a rearpropeller according to another embodiment of the present invention willnow be described. Elements having the same functions as those of theelements in the previous embodiments will be denoted by the samereference numerals and will not be described in detail.

Referring to FIGS. 15 to 19, a sealing device 1110 according to anotherembodiment of the present invention includes a pressurizing ring member1120 and a support ring member 1130 that are in surface contact witheach other in a sliding manner to enhance the sealing performance of thesealing device 1110 by preventing a sealing efficiency from beingdegraded even when the front propeller 10 and the rear propeller 20 thatrotate in opposite directions move in a direction of the radius of therotation shaft 5 due to non-uniform load applied thereto.

The pressurizing ring member 1120 is configured to apply pressureagainst the support ring member 1130. The pressurizing ring member 1120includes a fixing ring 1121 coupled to the hub 21 of the rear propeller20, a moving ring 1125 including a pressurizing unit 1123 that isdisposed apart from the fixing ring 1121 and that is in surface contactwith the support ring member 1130, and an elastic unit 1127 coupledbetween the fixing ring 1121 and the moving ring 1125 to apply pressureonto the moving ring 1125 toward the support ring member 1130.

The fixing ring 1121 is formed in a hollow cylindrical shape, and oneend of the fixing ring 1121 is fixedly coupled to the hub 21 of the rearpropeller 20 via a fixing member 1124 such as a bolt to form awatertight construction. The moving ring 1125 is spaced apart by apredetermined distance from the fixing ring 1121 in the axial directionof the rotation shaft 5, and has a hollow cylindrical shape surroundingthe outer surface of the rotation shaft 5.

The elastic unit 1127 includes a pair of fixing portions 1127 a and 1127b, both ends of which are coupled to an outer surface of the fixing ring1121 and an outer surface of the moving ring 1125 in a watertightconstruction so as to seal between the fixing ring 1121 and the movingring 1125, and a circular arc portion 1127 c connects the pair of fixingportions 1127 a and 1127 b and providing an elastic force.

That is, the pair of fixing portions 1127 a and 1127 b are pressurizedto be in contact with each other by a support 1127 d to form awatertight construction and are thus coupled to the outer surfaces ofthe fixing ring 1121 and the moving ring 1125, respectively. Thecircular arc portion 1127 c may be bent to a predetermined curvature toprovide an elastic force for pressurizing the moving ring 1125.

The elastic unit 1127 according to the present embodiment is not limitedthereto and various well-known means may be used as the elastic unit1127 provided that they can generate pressure applied toward the supportring member 1130.

The pressurizing unit 1123 may have a cylindrical shape and be coupledto a side of the moving ring 1125 to be detachable from the moving ring1125.

The pressurizing unit 1123 causes friction rotation to occur when it isin surface contact with the support ring member 1130, and is formed of amaterial having high wear resistance. A sliding surface 1123 a of thepressurizing unit 1123 that is in surface contact with the support ringmember 1130 may be formed to be perpendicular to the rotation shaft 5.

A sealing unit 1128 may be provided between the pressurizing unit 1123and the moving ring 1125 to prevent seawater from penetrating betweenthe pressurizing unit 1123 and the moving ring 1125.

Although the pressurizing unit 1123 is configured to be detachable fromthe moving ring 1125 in the present embodiment, the pressurizing unit1123 may be formed integrally with the moving ring 1125.

The support ring member 1130 has a cylindrical shape coupled to the hub11 of the front propeller 10 via a fixing member 1129 such as a bolt. Inthis case, support ring member 1130 is also coupled to the hub 11 of thefront propeller 10 to form a watertight construction.

A rear surface of the support ring member 1130 may be a sliding surface1131 formed in parallel with a direction perpendicular to the rotationshaft 5 to be in surface contact with the sliding surface 1123 a of thepressurizing unit 1123. The support ring member 1130 may be also formedof a material having high wear resistance.

Due to the above structure, even if the front propeller 10 and the rearpropeller 20 move in the direction of the radius of the rotation shaft 5due to a non-uniform load applied thereto, the sliding surface 1123 a ofthe pressurizing ring member 1120 and the sliding surface 1131 of thesupport ring member 1130 that are pressurized against each other to bein friction contact with each other in a sliding manner are capable ofabsorbing the movement of the front propeller 10 and the rear propeller20 in the direction of the radius of the rotation shaft 5, therebyenhancing the reliability of the sealing performance.

The sealing device 1110 performing a sealing function using frictionrotation by the sliding surfaces 1123 a and 1131 according to thepresent embodiment may be supplied a lubricant from a lubricant supplydevice 1140 loaded in the ship 1 to prevent the performance of thesealing device 1110 from being degraded due to frictional heat, asillustrated in FIG. 17.

The lubricant supply device 1140 includes a lubricant tank 1141 storinga lubricant, a lubricant supply line 1142 for supplying the lubricantfrom the lubricant tank 1141 to an inner space 1122 of the sealingdevice 1110, and a lubricant collecting line 1143 for collecting thelubricant from the inner space 1122 of the sealing device 1110.

The lubricant supply line 1142 is coupled to a lubricant supply path1150 formed in the rotation shaft 5. The lubricant collecting line 1143is coupled to a lubricant collecting path 1160 formed in the rotationshaft 5.

One end of the lubricant supply path 1150 may be coupled to a lubricantsupply unit 1151 installed on the rotation shaft 5, and another end oflubricant supply path 1150 may be coupled to the inner space 1122 formedbetween the rotation shaft 5 and the sealing device 1110 so as tocommunicate with the inner space 1122.

One end of the lubricant collecting path 1160 may be coupled to alubricant collecting unit 1161 installed on the rotation shaft 5, andanother end of the lubricant collecting path 1160 may be coupled to aconnecting fluid path 1170 formed in the hub 21 of the rear propeller 20to communicate with the connecting fluid path 1170.

The connecting fluid path 1170 is a pipe line connecting the lubricantcollecting path 1160 and the inner space 1122. One end 1171 of theconnecting fluid path 1170 may be connected to the inner space 1122, andanother end 1173 of the connecting fluid path 1170 may be connected toan opening hole 1162 formed in an end portion of the lubricantcollecting unit 1161.

Also, the other end 1173 (hereinafter referred to as a ‘communicationhole’) of the connecting fluid path 1170 connected to the opening hole1162 may have a width W2 that is greater than a width W1 of the openinghole 1162 as illustrated in FIG. 18.

As illustrated in FIG. 19, the length of the rotation shaft 5 is changeddue to thermal stress caused by seasonal variations and the change inthe length of the rotation shaft 5 results in a change in the locationof the opening hole 1162 connected to the communication hole 1173 whenthe rear propeller 20 is coupled to the rotation shaft 5. However, thechange in the location of opening hole 1162 may be compensated using thecommunication hole 1173 that is relatively wider.

The width W2 of the communication hole 1173 may be twice to four timesthe width W1 of the opening hole 1162.

Although the communication hole 1173 of the connecting fluid path 1170formed in the hub 21 of the rear propeller 20 is described as wider thanthe opening hole 1162 of the lubricant collecting path 1160 formed inthe rotation shaft 5 in the present embodiment, embodiments of thepresent invention are not limited thereto.

For example, various structures including a fluid path for supplying alubricant to a sealing device connected to a hub of a propeller via thehub of the propeller may be used.

That is, in a structure in which a fluid path 1160 through which alubricant flows (which is not limited to a lubricant collecting pathherein) is formed in the rotation shaft 5 and the connecting fluid path1170 connected to the fluid path 1160 is formed in the hub 21 of apropeller (which is not limited to a rear propeller), the communicationhole 1173 of the connecting fluid path 1170 connected to the openinghole 1162 of the fluid path 1160 is formed to be wider than the openinghole 1162.

Referring back to FIGS. 16 and 17, the lubricant supply device 1140 mayfurther include a pump 1144 and a cooling device 1145 that are installedat the lubricant supply line 1142, and a valve 1146, an oil separator1147, and a filter 1148 that are installed at the lubricant collectingline 1143.

The pump 1144 pumps a lubricant stored in the lubricant tank 1141,squeeze-pumps the lubricant to the lubricant supply unit 1151 via thelubricant supply line 1142. The lubricant pumped by the pump 1144 iscooled by the cooling device 1145 and transferred to the inner space1122 of the sealing device 1110 via the lubricant supply path 1150.

The lubricant transferred to the inner space 1122 cools the sealingdevice 1110, passes through the connecting fluid path 1170 and thelubricant collecting path 1160, and returns to the lubricant collectingline 1143 via the lubricant collecting unit 1161.

In this case, seawater may flow into the inner space 1122 of the sealingdevice 1110 via a gap between the sliding surfaces 1123 a and 1131. Theseawater flown into the inner space 1122 is mixed with the lubricant inthe inner space 1122 and collected via the lubricant collecting line1143.

The oil separator 1147 installed at the lubricant collecting line 1143separates the seawater from the lubricant mixed with the seawater.Foreign substances are removed from the lubricant from which theseawater is separated by the filter 1148, and the lubricant is collectedagain to the lubricant tank 1141.

Although the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, the present inventionis not limited thereto. It will be understood by those of ordinary skillin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention as definedby the appended claims.

1. A ship propelling apparatus comprising: a rotation shaft on which arear propeller is fixed; a front propeller rotatably supported on therotation shaft in front of the rear propeller; and a counter-rotatingdevice through which the rotation shaft passes, which includes a gearbox including therein a plurality of gears configured to reverserotation of the rotation shaft and transfer the reversed rotation to thefront propeller, and which is installed in an installation space formedat the rear of a ship, wherein the rotation shaft comprises: ameasurement hole formed to pass through a center of the rotation shaftfor centering of the counter-rotating device installed in theinstallation space; and an individual lubricant path separated from themeasurement hole.
 2. The ship propelling apparatus of claim 1, whereinthe counter-rotating device comprises: a first connector coupled to adrive flange provided on the rotation shaft so as to transfer arotational force of the rotation shaft to the plurality of gears; and asecond connector coupled to a hub of the front propeller to transferoutputs of the plurality of gears to the front propeller.
 3. The shippropelling apparatus of claim 2, wherein the plurality of gearscomprises: a drive bevel gear coupled to the first connector; a drivenbevel gear supported rotatably around the rotation shaft and coupled tothe second connector; and at least one reverse bevel gear configured toreverse rotation of the drive bevel gear and transfer the reversedrotation to the driven bevel gear.
 4. A ship propelling apparatuscomprising: a rear propeller fixed on a rotation shaft; a frontpropeller supported rotatably on the rotation shaft in front of the rearpropeller; and a counter-rotating device configured to reverse rotationof the rotation shaft and transfer the reversed rotation to the frontpropeller, wherein the counter-rotating device comprises a gear boxincluding therein a plurality of gears for reversing rotation of thefront propeller and accommodated in an installation space formed in atail of a ship, and a fixing flange provided at the front of the gearbox, and including a separation groove which is a through-groove,wherein the gear box is separated from the installation space byapplying a force to the gear box by inserting a bolt into the separationgroove.
 5. The ship propelling apparatus of claim 4, wherein a pluralityof separation grooves are formed along a marginal portion of the fixingflange that is in close contact with the gear box.
 6. The shippropelling apparatus of claim 5, further comprising a coupling memberwhich is coupled to the separation groove and into which a clamp bolt isinserted to fix the front of the gear box on the tail of the ship. 7.The ship propelling apparatus of claim 6, wherein the gear box isseparated from the installation space due to a force applied to the gearbox by the bolt inserted into the separation groove in a state in whichthe clamp bolt and the coupling member are loosened from the separationgroove.
 8. The ship propelling apparatus of claim 4, wherein a marginalportion of the fixing flange that is in close contact with the gear boxcomprises: clamp grooves into which clamp bolts are inserted to fix afront cover on the tail of the ship; and separation grooves formedalternately with the clamp grooves.
 9. The ship propelling apparatus ofclaim 8, wherein the gear box is separated from the installation spacedue to a force applied to the front cover by the bolts inserted into theseparation grooves in a state in which the clamp bolts are loosened fromthe clamp grooves.
 10. The ship propelling apparatus of claim 4, whereinthe fixing flange is coupled to the tail of the ship or formedintegrally with the tail of the ship.
 11. A ship propelling apparatuscomprising: a rear propeller fixed on a rotation shaft; a frontpropeller supported rotatably on the rotation shaft in front of the rearpropeller; a counter-rotating device including a plurality of gears forrevering rotation of the rotation shaft and transferring the reversedrotation to the front propeller, and accommodated in an installationspace formed in a tail of a ship; and a sealing device configured toseal between a hub of the front propeller and a hub of the rearpropeller, wherein the sealing device comprises: a pressurizing ringmember coupled to one of the hubs and configured to apply a pressurizingforce to the other hub; and a support ring member coupled to the otherhub, and configured to be in surface contact with the pressurizing ringmember in a sliding manner.
 12. The ship propelling apparatus of claim11, wherein the pressurizing ring member comprises: a fixing ringcoupled to one of the hubs; a moving ring disposed apart from the fixingring, and including a pressurizing unit that is in surface contact withthe support ring member; and an elastic unit coupled between the fixingring and the moving ring, and configured to apply a pressurizing forceto pressurize the moving ring toward the support ring member.
 13. Theship propelling apparatus of claim 12, wherein the pressurizing unit iscoupled to the moving ring to be detachable from the moving ring. 14.The ship propelling apparatus of claim 12, wherein a sliding surface ofthe pressurizing unit that is in surface contact with the support ringmember is perpendicular to the rotation shaft.
 15. The ship propellingapparatus of claim 12, wherein the elastic unit comprises: a pair offixing units, both ends of which are coupled to outer surfaces of thefixing ring and the moving ring; and a circular arc unit configured toconnect the pair of fixing units to apply the pressurizing force. 16.The ship propelling apparatus of claim 13, further comprising a sealingunit configured to seal between the moving ring and the pressurizingunit.